Do I need an alternator upgrade?

[jronnquist]

I know there are few things more annoying on a forum like this than someone starting a post with the line “I’m new here and just……”, so I’m hoping I’ve posted enough stuff of my own (and contributed enough to other posts) not to fall into this category. I’ve also spent the last three hours reading (and watching) up on this subject, so I do have at least some idea of what I’m talking about. That said, it hasn’t been enough to assure me one way or the other, and I’m hoping someone on here might have the experience and know-how to give me a little much-needed advice.

 

The Facts:

 

In the last 12 months I’ve replaced all of the OEM audio components on my 2007 Octavia VRS 170 Tdi PD. The last (and final) upgrade was a Kenwood 4-channel amplifier to run all four sets of door speakers. The full setup is as follows:

 

Head unit: Kenwood DDX4016DAB - http://www.kenwood-electronics.co.uk/car/nav_mm/mm/DDX4016DAB/?view=details

 

Sub: FLI Trap FT12A-F6 12” Active with built in amp (400W RMS – 1200W peak) - http://fliaudio.co.uk/portfolio/fli-trap-12-active/

 

Speakers: 4 x JBL Stage 600CE component sets (50W RMS – 150W peak) - http://uk.jbl.com/car-speakers/STAGE+600CE_.html?dwvar_STAGE 600CE___color=Black-EMEA#start=1

 

Amp: Kenwood KAC-8406 900Watt (4 x 70W RMS at 4 Ohms) - http://www.kenwood-electronics.co.uk/car/amp_spk/amp/KAC-8406/?view=details

 

The evolution has been a bit haphazard. The head unit was a surprise birthday present from my girlfriend that ended costing her another £50 once I told her (very gently) that it would be of little use without the OEM cable and CANBUS adapter. In hindsight, I’m not sure the CANBUS adapter was necessary as I’ve got no extras (steering wheel controls, etc) and the VCDS computer still complains about the missing OEM head unit every time I plug it in. Anyway, it was a huge improvement on the Stream MP3 unit in terms of functionality (DAB radio, USB, Bluetooth).

 

A few months later I had one of the rear door panels off for something else and noticed the mid-range speaker was completely seized up. I had also deluded myself into believing that I had decent speakers, but it was a bog-standard paper-cone piece of garbage, so I decided to upgrade them all. Using the “advertised” rating on the head unit of 50W per channel, I settled on the 70W (RMS) JBLs after erroneously concluding that the speaker wattage should ideally be a little higher than the amp output. The result was certainly an improvement, but I think this had more to do with the fact that BOTH rear mids were dead, and the fronts weren’t far behind.

 

Needless to say, I soon noticed a problem. It was only after scouring the manual of the head unit that I realised the output it boasted was only peak power, and that the RMS output was actually 22W per channel. At this point I did some research and concluded that a 900W (peak) amp with an RMS output of 70W per channel would be ideal. And so far this seems to be the case.

 

The Kenwood head unit has 3 coaxial outputs (left, right and sub) and the Kenwood amp has two coaxial inputs (left and right). I’ve managed to mount the amp inside the passenger footwell. It’s upside down and screwed to a piece of MDF, which in turn is mounted to the bottom of the AC fan housing. This means I have to remove it when I change the pollen filter, but if I mounted it under the passenger seat (as seems to be the standard place) it completely blocks the AC vents to the back on that side of the car. Mounting it where I did also meant I could run all 8 speaker wires straight to the inputs on the amp without extending then and only use 1M RCA cables to reach the head unit.

 

If anyone wants pictures of all this, give me a shout and I’ll add them to this thread.

 

This setup is obviously miles above the stock. I’ve matched the coax output level (4 volts) exactly on the Kenwood amp input. I’ve left the LPF and HPF settings off as both the JBL mids and tweeters have their own inline crossovers. I’ve also set the LPF on the sub down to 50Hz, which is where the JBLs leave off. And I’ve set the gain input to the sub low and am using none of the “bass boost”. I'm not sure why the sub doesn't have a volt-specific range for input (just a knob with no markings), but it might just be because it's cheap. 

 

Which brings me to my question; can the car’s existing alternator/battery setup deal with this?

 

If I was a "casual" listener, I probably wouldn’t bother asking, but I’m not. I’m a bit of a bass-head, and as soon as I get in the car (alone) the volume goes WAY up. Before I installed the Kenwood amp, I could get to between 24 and 28 on the volume button, but now it will quite happily go to the full 35 with no sign of deterioration in audio quality. I appreciate that  some of this has to do with the fact that I’ve set the coax volume to 4 volts, but I AM playing a LOT of loud music (with a LOT of bass). I know the components themselves can handle this, but can the car?

 

The combined RMS load of the 4-channel Kenwood amp and the FLI sub is 680 Watts (400W + 70W x 4). At 14 volts, that’s about 48 Amps of load on the battery. And although I can’t get a definite answer one way or another, I believe the OEM alternator is rated at between 90 and 110 Amps. I know the headlights alone draw 35 watts, so that doesn’t seem to leave a lot of headroom once you factor in the rest of the car’s “pre-upgrade” power needs. Now add in the fact that my listening habits are above modest and it’s unlikely that the 680 RMS watts is a realistic average. At peak power the sub and 4-channel amp draw 1200 and 900 watts respectively, which transates to 150 Amps at 14 volts. Even if we meet the difference halfway, we’re talking about 1390 watts, or 100 amps. Assuming my alternator is the 90 Amp one and it seems like I’m on a collision course with frequent amp cut-outs and a flat battery.

 

If this is indeed the case, adding a capacitor isn’t going to do anything from what I understand. And even upgrading the cables from the alternator (the “Big 3” as the yanks call it) won’t really be enough either.

 

Doing a quick search for alternators for the VRS, eurocarparts supply a TRX one rated at 140 Amps. Might this be what I need? Or have I worked myself into a completely pointless frenzy over all this? I’ve read so many forum threads on other sites suggesting that my modest set of components is well within the capacity of the car, and I’ve read just as many that insist I’m in trouble. Any – and I mean ANY – sound advice or pointers on this would be a godsend.

[jronnquist]

I should add here that I'm running the head unit equalizer at "flat", using NONE of the fancy enhancement settings, and the "sub output level" at zero (it goes from -50 to + something or other). I've also ignored all the LPF and HPF filter settings in the head unit menus. It's my understanding that all these settings are basically gimmicks. It is also my understanding that if you have a good quality source file and calilbrated hardware, the sound engineers in the studio have already done the work of making sure the music sounds the way it's supped, and that all the listener neeeds to do is play it.   

[Breezy_Pete]

You don't mention power feeds to your amps, what have you done, what are they fused at?

I think you'll find that your real current consumption is much lower than your calculated one, and so you'll be fine. 

[jronnquist]

I have separate direct feeds from the battery to both amps, each with a 60A in-line fuse.  

[Breezy_Pete]

If it were me and my multimeter, I'd whack it onto the 20A dc current range and stick it in circuit instead of each of these fuses, and measure the current directly.  If you start at low volume to check that it isn't outside the range of the meter, then crank it up gradually.  I think you may be surprised how little they really take.  Don't try this with an expensive multimeter unless you know how to change the fuse.

[jronnquist]

Had the multimeter on the batter today with all lights on, AC going full blast, wipers on full, and the sound system near full blast. It was reading a steady 14.1 volts, which I guess is a good sign. 

 

[ryan-re]

With the setup you have you dont need to upgrade the battery or alternator.

 

Its a pretty basic low power setup so no big upgrades are required.

 

With your voltage dropping to 14.1v means your alt is barely noticing it. Anything above 12.6 (this will be around the battery float voltage) is power from the alternator. So your battery isnt much.

 

As your power cable has a 60a fuse in it that means the total power your amps will take is 60a. 60x14.4 = 864watts @ 100% efficency. Your amps wont be that efficent, probably about 80% which is 691 watts. At 14.4v 691 watts is 48a. This will be at full power too which wont be all the time so this is why your 140a alternator isnt noticing your stereo making much of a difference.

 

If you did have issues with voltage drop the first things to change are

1. Upgrade power and earth cables (MUST be the same size)

2. Carry out TB3 upgrade. This is upgrading battery earth, engine earths and alternator to battery cables)

3. Upgrading the battery

4. Finally, if none of that helps upgrading the alternator. But you need to be running a lot of power to need that

 

 

[jronnquist]

Again, thank you very much for this. I actually have a separate power feed running to each amp with 60A fuses in them, so I guess that's even less reason to worry. 

[JonBRapid]

On 06/08/2017 at 23:06, jronnquist said:

Again, thank you very much for this. I actually have a separate power feed running to each amp with 60A fuses in them, so I guess that's even less reason to worry. 

Hi, your 60amp fuse might be a little high... are there any fuses in your amps???  if so your fuse should be that value otherwise you'll blow the fuse in the amp before the fuse next to the battery goes. I run one cable (with a fuse really close to the battery) then split this closer to the amps using a fused box. 

[ryan-re]

Jon. 

The fuse in the power cable is there to protect the cable it's self, not the amp. The fuse in the amp does that. 

 

A small 60a fuse in each of the power cable runs is fine